Blades are known to comprise an airfoil that projects in the hot gases path to guide the hot gases (guide vanes) or exchange mechanical power with the hot gases (rotor blades).
Moreover, blades also comprise platforms that close the space between adjacent airfoils and define a hot gases path.
As the hot gases are very hot (their temperature usually is greater than 1400° C.) the blades are always thermally highly loaded.
Thermal load causes differential deformations between the airfoil and platform that generate large forces that limit the blades service life.
EP 0764765 discloses a blade having an airfoil and a platform made in two separate pieces.
The connection between the airfoil and the platform is realized at their zone facing the hot gases path, i.e. in the same zone where the forces due to the deformations caused by the hot gases temperature are larger.
EP 1306523 discloses blades made of an airfoil and a platform in two separate pieces, but also in this case the connection between the airfoil and the platform is realized in their zone facing the hot gases path, because of the forces that during operation press the platform sides against the blade.
U.S. Pat. No. 5,248,240 discloses a stator vane assembly made of airfoils connected to a platform.
Also in this case the connection is realized in a zone of the airfoil and platform close to the hot gases path.
U.S. Pat. No. 6,331,217 discloses blades made of a plurality of crystal super-alloy pieces joined together across all the surfaces between the pieces.
Also in this case the connection between the pieces (and in particular between the pieces defining the airfoil and those defining the platform) is realized in zones close to the hot gases path.
U.S. Pat. No. 7,284,958 discloses a blade made of an airfoil and a platform at the two opposite sides of the airfoil. The platforms are connected to the airfoil also in its zone close to the hot gases path.
U.S. Pat. No. 2,656,146 discloses a further blade made of a platform having a through hole in which an airfoil is housed. Connection between platform and airfoil is established in the zone of the hole (i.e. close to the hot gases path).
As all the blades according to the prior art are joined (usually brazed but also other means are possible) in zones very close to the hot gases path, i.e. zones where the influence of the temperature of the hot gases flowing through the hot gases path is greater and causes large differential deformations, forces transmitted from the airfoil to platform and vice versa are consequently very large; this impairs the working life of the blades.